The microbial status of the flooded Intermediate and White's opencuts of the abandoned uranium mine at Rum Jungle was investigated by sampling the water column and sediments of several areas in each opencut. Smaller water bodies associated with the experimental heap-leach pile were also investigated. Several groups of bacteria were identified and population sizes were estimated using selective media techniques. Various physicochemical parameters of each sample were determined and correlated with the occurence of bacteria. Both opencuts although behaving differently were found to be heavily polluted by sulphuric acid and heavy metals White's more so than Intermediate. White's opencut was found to be stratified into an aerobic zone about five metres deep and a microaerophilic zone below this. Large populations of Thiobacillus ferrooxidans and autotrophic sulphur-oxidising bacteria indicated that degradation of sulphidic minerals in the walls and floors of the opencuts was still occurring. The isolation of T. ferrooxidans from sediments also containing anaerobic bacterial species suggested that T. ferrooxidans was degrading sulphidic minerals either anaerobically or microaerophilically. The smaller water bodies also were found to be heavily polluted by acid and heavy metals from drainage and seepage from the sulphidic heap-leach pile.